The proposed research seeks to determine the contribution of dopamine to the firing of neurons in the rat nucleus accumbens while the aimal self-administers cocaine. Dopamine. Psychostimulants, dopaine agonists and dopamine antagonists will be iontoporetically applied to recorded accumbens cell during the performance of a lever-pressing task that results in the delivery of a cocaine reward to the animal. Locailized iontophoretic application of drugs allows for their effects on individual neurons to be observed while the behavior of the the animals continues unchanges by the drug. The effects of these drugs on the firing of these cells during the lever-press and between repsonse will be analyzed to determine what role dopamine plays in the emergence, timing and shing of patterns of firing that are specifically associated with the lever-press. The results of these studies will indicate how dopamine modifies information processing in the accumbers, and will asuggest mechanisms by hopaminergic modulation of accumberns cell firing leads to the motivation to obtain the drug.